1. Field of the Invention
The present invention relates to an apparatus for recording and reproducing a disk-type storage medium with spiral tracks and also to a format of such a storage medium.
2. Description of the Prior Art
In the disk-type storage media such optical disks, optomagnetic disks, and the like, there are known two types one having concentric tracks and the other having spiral tracks. However, due to technical difficulty for forming fine-pitch concentric tracks with high precision, the spiral track type is generally used when a large storage capacity is required in a small-sized disk.
In sequential operations performed to record and reproduce data, there is a process called "seek", which is an operation to move a head to a desired recording/ reproducing position. In the case of the disk having the concentric tracks, the head is held on a track after a seek; while in the case of the disk having the spiral tracks, the head is advanced gradually toward the next track with rotation of the disk after a seek. Accordingly, for the disk having such spiral tracks, such a technique is used as returning the head to the desired track with reference to a specific signal called an "index signal". And this technique is generally called "track jump", "kick back" or "retrace".
A method of retrace is disclosed in Japanese Patent Laid-open No. 58 (1983)-115638, wherein however, no detailed description is given with respect to the problem described below.
FIG. 10 illustrates an exemplary format of a disk-type storage medium used for execution of a conventional retrace. In FIG. 10, spiral solid lines correspond to spiral tracks, and S0-S2 represent sectors shown by thick solid lines, on which data are stored. Succeeding sectors next to S2 are formed similarly up to the retrace area, but they are omitted in the figure. In this figure, one track is defined per rotation, and hereinafter it will be referred to as a "physical track".
A storage medium having the format of FIG. 10 is recorded and reproduced in the following manner. First, suppose that a target sector to be recorded or reproduced is S1 in an nth physical track (n: integer). A recording/reproducing apparatus executes the aforementioned seek for moving a head to the target sector. Completion of the seek is confirmed by reproduction of track address data stored in all sectors included in the nth physical track. After passage of the head through the rear end of the nth physical track after to completion of the seek, the head is driven to jump one track in the reverse direction so as to keep tracing the target physical track. The data of the sector S1 is recorded or reproduced by the head during tracing the nth physical track. However, the track jump at this time is limited merely to the retrace area shown in FIG. 10. An index signal for the retrace is detected from the storage medium.
As described above, in the use of a storage medium with spiral tracks, a specific retrace area is necessary in addition to the data storage area. The time required for such retrace is about 1 msec. Accordingly, in using the storage medium so formated as shown in FIG. 10, there exists a disadvantage that the area for storage of data becomes relatively smaller with increase of the disk rotation speed.
In one exemplary method for solving the above problem, the index signal is replaced by the track address data included in the content of the sector. In this method, however, there arises another problem that if a defective track exists, the track can never be traced again. This problem is rendered more conspicuous particularly when the format is not of pregroove type but soft type.